Magnetic transducer fabrication technique

ABSTRACT

There is described an efficient technique for simultaneously providing a large plurality of magnetic head cores with bonded gaps having reinforcing fillets.

United States Patent Weaver 1 Dec. 19, 1972 1541 MAGNETIC TRANSDUCER FABRICATION TECHNIQUE [72] Inventor: Harry Zane Weaver, Framingham,

Mass.

[73] Assignee: RCA Corporation [22] Filed: Nov. 19, 1970 [21] Appl. No.: 90,934

[52] US. Cl. ..29/603, 179/100.2 C [51] Int. Cl. ..'.....'.G1lb 5/42, H0lf7/06 [58] Field of Search 29/603; 179/1002 C;

346/74 MC; 340/174.1 F

[56} References Cited UNITED STATES PATENTS Manders ..29/603 3,479,738 11/1969 Hanak ..29/603 3,094,772 6/1963 Duinker ..29/603 3,579,214 5/1971 Solyst ....29/603 X 3,187,411 6/1965 Duinker et al.... ..29/603 3,104,455 9/1963 Frost ....29/603 3,229,355 1/1966 Hluszko ....29/603 3,605,259 9/1971 Tawara et a1. ....29/603 3,246,383 4/1966 Peloschek et a1 ..29/603 Primary Examiner'-John F. Campbell Assistant Examiner-Carl E. Hall Attorney-Edward J. Norton [5 7 ABSTRACT There is described an efficient technique for simultaneously providing a large plurality of magnetic head cores with bonded gaps having reinforcing fillets.

6 Claims, 6 Dravving Figures PATENTED DEC 19 I972 SHEET 1 [1F 2 r. Mm W W 2 m 8 H QWEW PATENIEUHEIZ I 9 m2 SHEET 2 OF 2 f Y e 5 w m WM W1: 8 H

MAGNETIC TRANSDUCER FABRICATION TECHNIQUE This invention relates to a simplified technique for providing magnetic transducer head cores.

In making magnetic transducer heads it is desirable to fabricate a large plurality of heads at one time, as this is more economical and results in substantially identically formed and interchangeable heads.

In the past loaves of magnetic material have been placed in confronting relation, bonded and severed at longitudinally spaced intervals to form a series of magnetic heads. When bonding the respective loaves to form pole pieces with a filled gap, it is important to provide a reinforcing fillet. The reinforcing fillet is provided behind or on the opposite side of the gap from the working surface of the head-core. The reinforcing fillet prevents damage to the pole pieces and gap when separating the loaf into individual head cores. It is necessary to avoid damage such as chipping, cracking or other modification of the head gap, as this would result in degraded signal response or generally unacceptable performance of the head. The gap reinforcing fillet also provides structural rigidity to the individual head when utilized separately.

In present methods of fabricating from loaves of magnetic material, where more than one series of fillet reinforced gaps are to be produced, it is necessary to bond and form the fillet for each series of gaps in separate operations such as by turning the load over. Since each bonding operation using material such as glass, takes appreciable time to prepare, heat andcure, it is extremely inefficient and wasteful to perform these operations separately for each head core to be produced.

These problems are solved by the technique of the present invention which makes possible the provision of a large plurality of bonded head core gaps with reinforcing fillets in a simplified single operation.

Briefly according to the invention, first and second loaves of magnetic material are provided. At least one of the loaves has a plurality of longitudinally spaced projections. Each of the projections has a tapered portion on the same given side of the respective projections. The loaves are placed in juxtaposed position with the spaced projections in confronting relation with portions of the second load to define a corresponding plurality of transducer gaps therebetween. Also formed in cooperation with adjacent portions of the loaves are tapered recesses which communicate with the gaps. The juxtaposed loaves are oriented so the gaps are arranged one above the other with the recesses being longitudinally constricted in the same direction as the direction of action of local gravitational force. Each of the plurality of gaps including the adjacent loaf portions are simultaneously bonded with a non-magnetic bonding material to provide a corresponding plurality of reinforcing fillets at the same given side of and communicating with the bonded gaps.

FIG. la & b are end views of an arrangement of magnetic loaves of material at different stages of fabrication of transducer head cores according to the invention.

FIG. 2 is a perspective view in section, of a portion of the arrangement of the loaves of FIG. 1.

FIG. 3 is a further perspective view of a loaf assembly according to the invention.

FIG. 4 is an enlarged view of a portion of a loaf assembly according to the invention.

FIG. 5 is an end view of a complete transducer head.

FIG. 1 shows in end view a series of loaves 2, 4 and 6 of suitable magnetic material, such as ferrite, for forming a plurality of magnetic transducer head cores. Each of the loaves 2, 4 and 6 have a height or dimension in the direction herein referred to as the longitudinal direction, which is appreciably greater than the width or thickness of the loaves. Further as shown in the perspective view of FIG. 3, each of the loaves 2, 4 and 6 are elongated transversely to the longitudinal direction, but have the same cross section throughout. The loaves 2 and 6 each have a plurality of longitudinally spaced projections 8 with surfaces 10. Each of the surfaces 10 is prepared in known manner to serve as a boundary wall of a transducing gap. Similarly the loaf 4 has a corresponding plurality of longitudinally spaced surface portions 12, each of which is also prepared in known manner to serve as a boundary wall of a transducing gap. The loaves 2, 4 and 6 are placed in juxtaposed relation as shown, with the surfaces 10 and 12 in confronting relation to define a corresponding plurality of transducing gaps 14. In each of the projections 8 of the loaves 2 and 6, the surface 16 to the same side of each gap thus defined, is shaped to provide a tapered recess 18. Each of the tapered recesses 18 are longitudinally constricted in the same direction as shown and communicate with their respective transducing gaps 14.

For bonding, the loaves 2, 4 and 6 are arranged in relative relation as shown in FIG. 1(a). While not shown for purposes of clarity in the drawing, any suitable form of clamping arrangement for holding the loaves 2, 4 and 6 in position can be used. More particularly the whole assembly of juxtaposed loaves 2, 4 and 6 with respective confronting surfaces 10 and 12 is oriented, such that the tapered recesses 18 are arranged one above the other in a vertical sense. That is the assembly of loaves 2, 4 and 6 is arranged, so that the direction of constriction of the tapere recesses 18 is generally in the vertically down or local direction of the force of gravity which is indicated by the arrow 20.

In one method a spacer or shim 21, for example of stainless steel 50-100 p. inches thick is placed so as to be disposed between each of the confronting surfaces 10 and 12 in the vicinity of the end portions of the elongated loaf 2, 4 and 6. The spacers 21 are shown by way of example in FIG. 3 and have a height or extent in the longitudinal direction which is at least sufficient to pass through each of the gaps 14 of the loaves 2, 4 and 6. For a loaf with an elongated dimension of say 0.8 inches, the spacers 21 may extend approximately 0.050 inches along the loaves 2, 4 and 6.

As shown in FIG. 1(a) a non-magnetic bonding material 22, such as one of many known types of glass used for bonding magnetic materials, is disposed in each of the recesses 18. The bonding material 22 extends between the end shims 21 along the elongated extent of the loaves 2, 4 and 6. The amount of bonding material 22 disposed in each recess 18 is of a volume sufficient to fill the gaps 14 and provide a residual portion of the bonding material 22. The assembly of loaves 2, 4 and 6, while oriented as just described by suitable means, not shown, is then heated with pressure exerted in the direction of arrows 23 for a sufficient time to cause the particular bonding material 22 utilized to flow freely. Bonding glasses witha melting temperature in the range of 600 900C and a pressure of for example 2000 psi have been found suitable for practicing the invention. While exerting the indicated pressure, the temperature of the assembled loaves is elevated from room temperature to the indicated bonding material melting point range in about 15-20 minutes and held there for approximately 15 min. Due to the described shape, relative relation and vertical orientation of the loaves 2, 4 and 6, the bonding material 22 is caused by gravitational forces to simultaneously flow into all of the gaps 14. Where the gaps 14 are as usual relatively narrow, for example several micro-inches, the flow of a bonding material is assisted by capillary action in the gaps 14.- As shown in FIG. 1(b) the tapered recesses 18 cause the residual volume of bonding material 22, to

simultaneously form a corresponding plurality of fillets 24 between the loaves 2, 4 and 6 which communicate with the respective gaps 14. In FIG. 1(b) the loaf portion containing the shims is removed to more clearly show the resultant bonded gaps and fillets. As shown in section in FIG. 2, the fillets 24 extend throughout the loaves 2, 4 and 6. The heat is then removed from the assembly of loaves 2, 4 and 6 and they are allowed to cool to room temperature, which may for example take about one hour. If desired other suitable curing procedures are performed. The result is the simultaneous provision of a large number of bonded, gap filled and fillet reinforced head cores.

In an alternative bonding method, before the loaves are arranged for bonding as described, there is first deposited by known techniques alternate layers of glass and aluminum oxide A1 on each of the surfaces and 12 throughout the elongated extent of the loaves 2, 4 and 6. FIG. 4 shows a portion of the loaves 2, 4 and 6 with the alternating layers of glass 25 and aluminum oxide 27 built up on each of the surfaces 10 and 12. The glass 25 may also be of a type whose melting point is in the range of 600-900C. With the loaves 2, 4 and 6 aligned as described, again a suitable bonding material 29 is disposed in the recesses 18. For this method it is not necessary to employ shims 2. If the bonding material 29 is glass, it should be selected to have a melting point no greater and preferably somewhat lower than the glass 25. The glass 29 extends along the entire extent of the recesses 18 of the elongated loaves 2, 4 and 6. The assembled loaves 2, 4 and 6 with the bonding material 29 and alternate layers of glass 25 and aluminum oxide 27 are then simultaneously heated under the influence of a pressure urging the loaves together. A sufficient quantity of bonding material 29 is utilized to bridge the recesses 18 to form a reinforcing fillet between the loaves. The pressures, temperatures and times for the first bonding method described are also suitable for the just described alternative bonding method. The result is the glass 25 bonds the aluminum oxide layer 27 to the respective loaf surfaces 10 and 12, with the bonding material 29 again forming reinforcing fillets to one side of the bonded gaps. The resultant gap is substantially determined by the thickness of the aluminum oxide layer 27, which may be for example 25 micro-inches thick. For a layer 27 of 25 micro-inches the glass layers 25 may be on the order of 2 microinches. Again there is simultaneously provided in a simple operation, a large number of bonded, gap filled, and fillet reinforced head cores.

indicated for example by the dashed lines 28 of H0. 2.

FIG. 5 shows an example of an individual head core 30 separated from the loaf assembly shown in FIGS.

14. To form an operatable transducer, a bar or strip of suitablemagnetic material 32 is secured to intercouple the free ends of the core to complete themagnetic circuit. As shown, exciting coils 34 may be made to encircle portions of the cores. I

What is claimed is:

l. A method for simultaneously producing a plurality of separable bonded head cores with gap reinforcing fillets, comprising the steps of: providing first and second loaves of magnetic material with gap defining portions, said gap defining portions of said first loaf in cluding a plurality of longitudinally spaced projections; with each of said projections including a first surface substantially defining the surface of cooperation with a record medium for said core to be provided, a second surface intersecting said first surface to define a first gap defining edge of said second surface, and a further surface inclined with respect to said second surface and intersecting said second surface to define a second gap defining edge of said second surface which is opposite said first gap defining edge of said second surface, said second gap defining edge of said second surface determining the extent of the depth of said gap with respect to said first surface; placing said first and second loaves in juxtaposed position with said gap defining surfaces of said spaced projections of said first loaf in confronting relation with said gap defining portions of said second loaf to define a corresponding plurality of transducer gaps of a given dimension in the direction therebetween and forming in cooperation with adjacent portions of said loaves tapered recesses between said loaves which communicate with said gaps, said tapered recesses having a dimension in the direction between said loaves which exceeds said given dimension of said gaps; orientating said juxtaposed first and second loaves so that said gaps are arranged one above the other with said tapered recesses being longitudinally constricted in the same direction of action of local gravitational force; and simultaneously bonding with a non-magnetic material each those gap defining surfaces in confronting relationship, which define said plurality of gaps, and the adjacent loaf portions forming said tapered recesses, to provide a corresponding plurality of reinforcing fillet bonds between said loaves at the same given side of and communicating with the respective ones of said plurality of bonded gaps.

2. The invention according to claim I and further including the step of; separating said bonded loaves into selected portions, each of said selected portions including a bonded gap and reinforcing fillet between adjacent portions of said loaves.

3. The invention according to claim 1, including the steps of: disposing an amount of non-magnetic bonding material in the vicinity of the point of communication of each of said tapered recesses with the respective gaps, the amount of bonding material being sufficient to fill said gap and provide a residual amount in said recess; and simultaneously heating said loaves and each amount of said bonding material to a temperature sufficient to cause flow of said material, and for a time sufficient to allow said material to fill said gaps, said residual amount of bonding material forming said reinforcing fillets in said recesses.

4. The invention according to claim 1, wherein; prior to the step of juxtaposing said first and second loaves, depositing on each of said gap defining portions of said first and second loaves a first layer of a glass bonding material, depositing on each of said first layers a second layer of aluminum oxide, and depositing on each of said second layers a further layer of glass bonding material.

5. A method for simultaneously producing a plurality of separable bonded head cores with gap reinforcing fillets, comprising the steps of: providing first and second loaves of a magnetic ferrite material with gap defining portions, said gap defining portions of said first loaf including a plurality of longitudinal spaced projections, each of said projections including a first surface substantially defining the surface of cooperation with a record medium for said core to be provided, a second surface intersecting said first surface to define a first gap defining edge of said second surface, and a further surface inclined with respect to said second surface and intersecting said second surface to define a second gap defining edge of said second surface which is opposite said first gap defining edge of said second surface, said second gap defining edge of said second surface determining the extent of the depth of said gap with respect to said first surface; placing said first and second loaves in juxtaposed position with said gap defining surfaces of said spaced projections of said first'loaf in confronting relation with said gap defining surfaces of said second loaf, providing between said confronting loaves means for establishing a given dimension in a direction between said gap defining portions of said loaves to form a corresponding plurality of transducer gaps therebetween and forming in cooperation with adjacent portions of said loaves tapered recesses between said loaves which communicate with said gaps, said tapered recesses having a dimension in the direction between said loaves which exceeds said given dimension of said gaps; orientating said juxtaposed first and second loaves so that said gaps are arranged one above the other with said tapered recesses being longitu-- dinally constricted in the same direction of action of local gravitational force; placing a glass bonding material in each of said tapered recesses, said glass bonding material having a melting point in the range of 600-900 first C; applying pressure in a direction oint of said lass bonding material for a period of at east 15 mmu es, and thereafter said heat is removed and said composite assembly is allowed to cool to approximately room temperature. 

1. A method for simultaneously producing a plurality of separable bonded head cores with gap reinforcing fillets, comprising the steps of: providing first and second loaves of magnetic material with gap defining portions, said gap defining portions of said first loaf including a plurality of longitudinally spaced projections; with each of said projections including a first surface substantially defining the surface of cooperation with a record medium for said core to be provided, a second surface intersecting said first surface to define a first gap defining edge of said second surface, and a further surface inclined with respect to said second surface and intersecting said second surface to define a second gap defining edge of said second surface which is opposite said first gap defining edge of said second surface, said second gap defining edge of said second surface determining the extent of the depth of said gap with respect to said first surface; placing said first and second loaves in juxtaposed position with said gap defining surfaces of said spaced projections of said first loaf in confronting relation with said gap defining portions of said second loaf to define a corresponding plurality of transducer gaps of a given dimension in the direction therebetween and forming in cooperation with adjacent portions of said loaves tapered recesses between said loaves which communicate with said gaps, said tapered recesses having a dimension in the direction between said loaves which exceeds said given dimension of said gaps; orientating said juxtaposed first and second loaves so that said gaps are arranged one above the other with said tapered recesses being longitudinally constricted in the same direction of action of local gravitational force; and simultaneously bonding with a non-magnetic material each those gap defining surfaces in confronting relationship, which define said plurality of gaps, and the adjacent loaf portions forming said tapered recesses, to provide a corresponding plurality of reinforcing fillet bonds between said loaves at the same given side of and communicating with the respective ones of said plurality of bonded gaps.
 2. The invention according to claim 1, and further including the step of; separating said bonded loaves into selected portions, each of said selected portions including a bonded gap and reinforcing fillet between adjacent portions of said loaves.
 3. The invention according to claim 1, including the steps of: disposing an amount of non-magnetic bonding material in the vicinity of the point of communication of each of said tapered recesses with the respective gaps, the amount of bonding material being sufficient to fill said gap and provide a residual amount in said recess; and simultaneously heating said loaves and each amount of said bonding material to a temperature sufficient to cause flow of said material, and for a time sufficient to allow said material to fill said gaps, said residual amount of bonding material forming said reinforcing fillets in said recesses.
 4. The invention according to claim 1, wherein; prior to the step of juxtaposing said first and second loaves, depositing on each of said gap defining portions of said first and second loaves a first layer of a glass bonding material, depositing on each of said first layers a second layer of aluminum oxide, and depositing on each of said second layers a further layer of glass bonding material.
 5. A method for simultaneously producing a plurality of separable bonded head cores with gap reinforcing fillets, comprising the stepS of: providing first and second loaves of a magnetic ferrite material with gap defining portions, said gap defining portions of said first loaf including a plurality of longitudinal spaced projections, each of said projections including a first surface substantially defining the surface of cooperation with a record medium for said core to be provided, a second surface intersecting said first surface to define a first gap defining edge of said second surface, and a further surface inclined with respect to said second surface and intersecting said second surface to define a second gap defining edge of said second surface which is opposite said first gap defining edge of said second surface, said second gap defining edge of said second surface determining the extent of the depth of said gap with respect to said first surface; placing said first and second loaves in juxtaposed position with said gap defining surfaces of said spaced projections of said first loaf in confronting relation with said gap defining surfaces of said second loaf, providing between said confronting loaves means for establishing a given dimension in a direction between said gap defining portions of said loaves to form a corresponding plurality of transducer gaps therebetween and forming in cooperation with adjacent portions of said loaves tapered recesses between said loaves which communicate with said gaps, said tapered recesses having a dimension in the direction between said loaves which exceeds said given dimension of said gaps; orientating said juxtaposed first and second loaves so that said gaps are arranged one above the other with said tapered recesses being longitudinally constricted in the same direction of action of local gravitational force; placing a glass bonding material in each of said tapered recesses, said glass bonding material having a melting point in the range of 600-900*C; applying pressure in a direction urging said first and second loaves together; and while applying said pressure, heating the composite assembly to a temperature sufficient to melt said glass, simultaneously causing those gap defining surfaces in confronting relationship, which define said plurality of gaps, to be bonded and providing corresponding reinforcing fillets in each of said recesses.
 6. The invention according to claim 5, wherein; in said heating step, the temperature is held at the melting point of said glass bonding material for a period of at least 15 minutes, and thereafter said heat is removed and said composite assembly is allowed to cool to approximately room temperature. 